Novel intersection treatment scrutinized

MU Engineering researchers work onsite collecting data on the j-turn intersection at U.S. Highway 63 and Deer Park Road. From left are Igor Caus, a recent graduate who earned a bachelor’s degree in civil engineering in May; Kevin Koines, a rising senior in civil engineering; and Henry Brown, a research engineer in civil engineering.

In an effort to increase motorist safety and traffic-flow efficiency, the Missouri Department of Transportation (MoDOT) has implemented some novel intersection treatments on the state’s roadways. Two of these designs have been selected for implementation on roadways in or near Columbia. A “j-turn” constructed on U.S. Highway 63 and Deer Park Road south of Columbia has been operational since August of last year, and a “diverging diamond” at the Stadium Boulevard and Interstate 70 interchange is scheduled for completion late this fall.

A research team headed by Praveen Edara, MU assistant professor of civil and environmental engineering, was selected by MoDOT to evaluate the j-turn, a project being managed by Sawyer Breslow, a master’s student in Edara’s lab who will write his thesis on the project.

A conventional left turn onto a divided highway would require drivers to cross up to three lanes of traffic on U.S. Highway 63, as illustrated in the top image. A j-turn intersection would require drivers to turn left, then make a U-turn and merge, as shown on the bottom.

“Traffic on Highway 63 runs at 70 miles per hour,” Edara said. “Motorists making a left turn from a side street must look for gaps in both directions of 63. Any misjudging of gaps could lead to severe right angle crashes. MoDOT is using the j-turn to improve safety of such left turn movements on high-speed rural highways.”

The j-turn requires left-turning motorists from both directions to first turn right and then make a u-turn “downstream” to merge into traffic in the direction they intend to travel. Critics complain that j-turns add drive time, but advocates argue it may actually reduce it during peak traffic-flow since motorists will not have to wait for a safe gap in order to cross traffic.

“Even with a minor increase in travel time, the increased safety of j-turns makes them desirable, especially at locations with a history of angle crashes,” Edara said.

The issue is of special concern in Midwest states where rural expressways are prevalent, and the researchers believe study results will support MoDOT’s decision to install a j-turn on Hwy. 63.

Assistant Professor Praveen Edara

“We’re looking at a couple of things,” said Breslow, who led a team of students to gather data at the site using video monitoring and speed radar equipment. “How do people actually operate through them? Are they confused? How long are they waiting in the acceleration lane to merge?

“We’re also measuring some innovative safety measures such as gap availability, time to collision and time to intersection — things that have not been measured at other j-turn sites in the country. Our work will be an original contribution to the body of work on j-turn evaluations.” Breslow said.

Sawyer Breslow

Edara said that since the group was not able to monitor the Hwy. 63 site before the j-turn was installed, they requested a control site for comparison.

“MoDOT recommended the intersection of Highway 63 and Calvert Hill Road as a control,” Edara said. “Using it as a comparison, we can actually demonstrate how well the j-turn is working.”